Your position at time [tex]t[/tex], relative to the stop line:
[tex]x_1=-15\,\mathrm m+\left(10\dfrac{\rm m}{\rm s}\right)t[/tex]
The Porsche's position:
[tex]x_2=\dfrac12\left(3\dfrac{\rm m}{\mathrm s^2}\right)t^2[/tex]
a. You pass the Porsche immediately after the time it takes for [tex]x_1=x_2[/tex]:
[tex]-15\,\mathrm m+\left(10\dfrac{\rm m}{\rm s}\right)t=\dfrac12\left(3\dfrac{\rm m}{\mathrm s^2}\right)t^2\implies t=2.3\,\rm s[/tex]
at which point you both will have traveled 7.8 m from the stop line.
b. The equation in part (a) has two solutions. The Porsche passes you at the second solution of about [tex]t=4.4\,\rm s[/tex], at which point you both will have traveled 29 m.
c. At time [tex]t[/tex], the Porsche is moving at velocity
[tex]v=\left(3\dfrac{\rm m}{\mathrm s^2}\right)t[/tex]
so that at the moment it passes you, its speed is 13 m/s, which is about 46.8 km/h and below the speed limit, so neither of you will be pulled over.
